Why do covalent crystals typically have a much lower packing density than
metal crystals?
could it be something about attractive forces? https://www.quora.com/Why-are-covalently-bonded-materials-generally-less-dense-than-ionically-or-metallically-bonded-ones
Thanks
Why do covalent crystals have lower packing efficiency
Ans
Covalent crystals typically have a lower packing density than metal crystals due to the nature of their bonding. In covalent bonds, atoms share electrons, forming a network or lattice structure. This results in a three-dimensional arrangement of atoms, where each atom is bonded to several other atoms.
To understand why covalent crystals have lower packing densities, we can examine the factors that influence packing density:
1. Size of atoms: Covalent crystals often consist of larger atoms with more electrons compared to metal crystals. These larger atoms occupy more space, resulting in larger interatomic distances and lower packing densities.
2. Bonding nature: In covalent crystals, atoms are held together by strong covalent bonds, which require a fixed number of neighboring atoms to complete the electron sharing. This fixed coordination number limits the number of atoms that can be closely packed around each atom, reducing the packing density.
3. Void spaces: The presence of void spaces or empty pockets between atoms in the lattice structure of covalent crystals also contributes to lower packing densities. These void spaces arise due to the specific arrangement and angles of covalent bonds.
To calculate the packing density of a crystal, you can use the formula:
Packing density = (Volume of atoms) / (Total volume of the unit cell),
where the volume of atoms is determined based on the size of the atoms and the total volume of the unit cell is calculated by multiplying the dimensions of the unit cell.
In summary, covalent crystals have lower packing densities compared to metal crystals because of the larger size of atoms, the nature of covalent bonding, and the presence of void spaces within the lattice structure.